Oligonucleotide immobilization in μL drops. Humidity dependence. Mean fluorescence intensities after 120 min immobilization of 2 μM solutions of aACG and ACG on 2D epoxy and 3D hydrogel surface, respectively, in 1 μL drops. Slides were kept in the dark at 20% and 100% relative humidity. Measurements were performed with the same scanner settings as applied in the nL experiments to allow comparing intensities.